1. Field of the Invention
The present invention relates to a wafer processing method such as plasma dicing.
2. Description of the Related Art
Usually, a dicing saw or a laser processing apparatus is used to divide a semiconductor wafer. The dicing saw performs a crushing action and accordingly tends to cause chipping of the wafer. Accordingly, the dicing saw has a problem that the die strength of each chip obtained by dividing the wafer is reduced. The dicing saw has another problem that the processing time is relatively long. On the other hand, the laser processing apparatus has such a merit that chipping is less caused in cutting the wafer and the width of a cut area is very small. However, since the chips (devices) are arranged close to each other, there is a problem such that the chips may come into contact with each other during transfer of the wafer to the subsequent step, causing chipping.
To cope with these problems, there has been proposed a processing method (plasma dicing) of dividing a wafer into individual chips by using plasma etching (see Japanese Patent Laid-open No. 2006-114825, for example). This processing method has a merit such that even when the diameter of the wafer is large, the processing time for formation of grooves on the wafer is hardly increased and the die strength of each chip can be improved. In the plasma dicing described in Japanese Patent Laid-open No. 2006-114825, each device not to be etched is preliminarily protected by a resist film, and only the division lines are subjected to plasma etching to thereby form a division groove along each division line. After finishing the plasma etching, the resist film is removed to expose the devices. Usually, the removal of the resist film modified by the plasma etching is performed by ashing (dry etching) using oxygen plasma.